Junai Tokkou Taichou!

From Tokyopop:

When the school's two biggest troublemakers get into a tussle, there's nothing left for them to do but fall in love! In Love Attack, you'll find a rollicking brawl of a good time as the roughest guy and girl in school get themselves into trouble--and find themselves in love.

Chiemi Yusa's high-school record is far from perfect. She's already been suspended twice for fighting, and she's not even half-way through her first year! In danger of getting expelled for starting yet another brawl, her teacher approaches her with an unexpected offer: get her classmate Akifumi 'Deranged Devil' Hirata, the nastiest fighter in the whole school, to clean up his act, and her record will officially be cleared. Reluctantly she accepts, and immediately goes on the attack. But as she's waiting for him to retaliate, she discovers that he has more in store for her than just a fight! From the creator of Girl Got Game and Heaven!! comes a rollicking brawl of a good time as the roughest guy and girl in school get themselves into trouble--and find themselves in love.

From the author:

Spoiler (mouse over to view) This is the story of how Hirata-san (whom Kyou met when she ran away in Vol.9 Ch. 32 of "Power!!") met his wife. It was supposed to end after one chapter, but somehow it was decided that it would be continued.